The present invention relates to a facsimile machine and a TCF (Training Check Field) reception method for a facsimile machine, and in particular, to a facsimile machine and a TCF reception method for a facsimile machine which utilize EIA 578 facsimile control commands (AT commands) and which operate according to timing defined in ITU-T T.30.
Among various types of information communication means provided today, information communication by facsimile has a strong point in that text, characters, images or whatever on a sheet can be transmitted easily and directly, and facsimile machines have come into wide use in many countries.
A facsimile machine generally comprises a fax/modem section as the interface of the facsimile machine to a public network circuit such as a public switched telephone network and a computer unit etc. for executing processing of data (received data or data to be transmitted) and outputting AT commands to the fax/modem section.
In the following, an example of a conventional facsimile machine and a conventional TCF reception method for a facsimile machine will be described referring to FIG. 1 through FIG. 4. Incidentally, FIG. 2 through FIG. 4 will also be used later for explaining a facsimile machine and a TCF reception method for a facsimile machine in accordance with the present invention.
Referring to FIG. 2, the conventional facsimile machine is composed of a computer unit 1 which operates according to control of a program and outputs AT commands, and a fax/modem 2 which is connected to a communication line. The fax/modem 2 includes an AT command execution analysis section 21 and a signal processing section 22. The AT command execution analysis section 21 and the signal processing section 22 are realized by, for example, one or more microprocessor units which are composed of one or more CPUs (Central Processing Units), ROM (Read Only Memory), RAM (Random Access Memory), etc.
Incidentally, while the computer unit 1 and the fax/modem 2 are provided apart in FIG. 2, of course, the computer unit 1 and the fax/modem 2 can also be installed in one body as an integral-type facsimile machine. In addition, while the hardware fax/modem 2 is employed as the fax/modem section of the facsimile machine in FIG. 2, the fax/modem section is not limited to such a hardware fax/modem section and it is also possible to realize the fax/modem 2 by software that is installed on a computer (for example, the computer unit 1) and executed by a CPU of the computer.
In the following, the operation of the components of the conventional facsimile machine shown in FIG. 2 will be explained.
The computer unit 1 sends AT commands to the fax/modem 2 and thereby instructs the fax/modem 2 to execute sending or reception of a fax. The AT command execution analysis section 21 in the fax/modem 2 analyzes an AT commands sent from the computer unit 1 and executes the AT commands. The signal processing section 22 executes transmission of signals to the communication line or reception of signals from the communication line.
FIG. 1 is a schematic diagram showing changes of states of the fax/modem section in the conventional facsimile machine. Referring to FIG. 1, the internal state of the conventional fax/modem section can roughly be classified into an AT command standby state (state #1) in which the fax/modem section waits for supply of an AT command from the computer unit 1 and an AT command execution state (state #2) in which the fax/modem section executes an AT command. For example, the conventional fax/modem section is in the state #2 when the fax/modem section is receiving a DCS (Digital Command Signal) via the communication line, and changes into the state #1 (AT command standby state) after finishing reception of the DCS. After receiving an AT command (which instructs the fax/modem section to receive a TCF) from the computer unit 1, the conventional fax/modem section changes into the state #2 and executes a TCF reception process.
As described above, the internal state of the conventional fax/modem section includes the state #1 and the state #2, and the fax/modem section is in the state #1 or in the state #2 at a moment.
In the following, the operation for sending and receiving signals employed in the conventional facsimile machine and the conventional TCF reception method will be described referring to figures.
FIG. 3 is a timing chart showing an example of signals which are sent via the communication line and received by the fax/modem 2. The signals shown in FIG. 3 are signals according to ITU-T T.30, including a TSI (Terminal System Identifier) 201, a DCS (Digital Command Signal) 203 and a TCF (Training Check Field) 205. The above acronyms will be used in the same meanings throughout the document and figures.
When the signals shown in FIG. 3 are received by the fax/modem 2, commands and responses shown in FIG. 4 are communicated between the computer unit 1 and the fax/modem 2. FIG. 4 is a schematic diagram showing an example of input AT commands and response AT commands which are received and transmitted by the fax/modem 2.
Referring to FIG.4, the AT command xe2x80x9cAT+FRH=3xe2x80x9d (command 301) is a command for instructing the fax/modem 2 to receive an HDLC frame, and the AT command xe2x80x9cAT+FRM=96xe2x80x9d (command 303) is a command for instructing the fax/modem 2 to receive a TCF. Here, the HDLC frame is a frame according to HDLC (High Level Data Link Control Procedure).
In the example shown in FIG. 2, the AT commands sent from the computer unit 1 are received and accepted by the AT command execution analysis section 21 of the fax/modem 2. When the signal processing section 22 of the fax/modem 2 detected a carrier of the HDLC frame, the AT command execution analysis section 21 sends back a command 305 which means xe2x80x9cCONNECTxe2x80x9d to the computer unit 1 as a response to the command 301. After the signal processing section 22 received the HDLC frame, the AT command execution analysis section 21 sends the HDLC frame to the computer unit 1. When the signal processing section 22 detected end of data, the AT command execution analysis section 21 sends a command 307 which means xe2x80x9cOKxe2x80x9d to the computer unit 1. When the signal processing section 22 detected a carrier of the TCF, the AT command execution analysis section 21 sends back a command 309 which means xe2x80x9cCONNECT xe2x80x9d to the computer unit 1 as a response to the command 303. After the signal processing section 22 received the TCF, the AT command execution analysis section 21 sends the TCF to the computer unit 1. When the signal processing section 22 detected end of data, the AT command execution analysis section 21 sends a command 311 which means xe2x80x9cNO CARRIERxe2x80x9d to the computer unit 1.
As described above, in the conventional facsimile machine and the conventional TCF reception method for a facsimile machine, the fax/modem 2 is supposed to execute transmission of signals to the communication line and reception of signals from the communication line correctly, by communicating AT commands with the computer unit 1.
However, there exist some types of facsimile machines whose switching time between the HDLC frame and the TCF (i.e. time interval between finishing sending the HDLC frame and starting sending the TCF) is almost the same as the minimum interval which is allowed in the ITU-T T.30.
In the case where such a facsimile machine sends the above signals to the conventional facsimile machine which employs the conventional TCF reception method (i.e. which operates as has been explained referring to FIG. 4), the conventional facsimile machine can not always establish communication with the facsimile machine, since the time interval is not enough.
Referring again to FIG. 4, the command 307 indicating a response xe2x80x9cOKxe2x80x9d to the command 301 (xe2x80x9cAF+FRH=3xe2x80x9d: requesting reception of an HDLC frame) is transmitted by the fax/modem 2 to the computer unit 1 when the signal processing section 22 shown in FIG. 2 completed reception of the whole data of the HDLC frame.
Therefore, the command 307 indicating the response xe2x80x9cOKxe2x80x9d is transmitted by the fax/modem 2 to the computer unit 1 at the point xe2x80x9c1xe2x80x9d in the timing chart of FIG. 3.
When the computer unit 1 received the command 307 indicating the response xe2x80x9cOKxe2x80x9d, the computer unit 1 sends the command 303 (the xe2x80x9cAT+FRM=96xe2x80x9d requesting reception of a TCF) to the fax/modem 2. The point xe2x80x9c2xe2x80x9d in the timing chart of FIG. 3 corresponds to the point when the command 303 is transmitted by the computer unit 1.
However, in the case where the facsimile machine (whose switching time between the HDLC frame and the TCF is very short) sent the signals to the conventional facsimile machine, the point when the command 303 is transmitted by the computer unit 1 comes to the point xe2x80x9c3xe2x80x9d in FIG. 3 due to the short switching time.
In such cases, the command 303 reaches the fax/modem 2 after arrival of the front end of the TCF, and thus the fax/modem 2 can not receive the TCF correctly.
In the ITU-T T.30, the switching time between the HDLC frame and the TCF is required to be 75 ms or more. Therefore, in order to let the fax/modem 2 always receive the TCF correctly, the computer unit 1 in FIG. 2 is required to output the command 303 (the xe2x80x9cAT+FRM=96xe2x80x9d requesting reception of a TCF) 75 ms or less after the reception of the command 307 indicating the response xe2x80x9cOKxe2x80x9d.
However, as a matter of fact, it is very difficult to reduce the time interval between reception of the command 307 and sending of the command 303 to less than 75 ms, because of efficiency of the computer unit 1 and the interface between the computer unit 1 and the fax/modem 2.
Therefore, the conventional facsimile machine and the conventional TCF reception method for a facsimile machine involve a problem of being unable to establish communication with the facsimile machines whose switching time between the HDLC frame and the TCF is very short, by missing the front end of the TCF.
It is therefore the primary object of the present invention to provide a facsimile machine, by which a TCF (Training Check Field) following a DCS (Digital Command Signal) of an HDLC frame can be received with reliability, and thereby establishment of communication is ensured and communication reliability is secured.
Another object of the present invention is to provide a TCF reception method for a facsimile machine, by which a TCF (Training Check Field) following a DCS (Digital Command Signal) of an HDLC frame can be received with reliability, and thereby establishment of communication is ensured and communication reliability is secured.
In accordance with a first aspect of the present invention, there is provided a facsimile machine for sending and receiving a fax comprising a fax/modem means. The fax/modem means changes into a state for receiving a TCF (Training Check Field) if the fax/modem means received a DCS (Digital Command Signal), regardless of whether or not the fax/modem means has already received a TCF reception command.
In accordance with a second aspect of the present invention, there is provided a facsimile machine for sending and receiving a fax, comprising a fax/modem means for communicating signals with a communication line in order to sending and receiving a fax and an AT command output means for outputting AT commands such as a DCS reception command for requesting reception of a DCS (Digital Command Signal) and a TCF reception command for requesting reception of a TCF (Training Check Field) to the fax/modem means. The fax/modem means changes into a state for receiving a TCF if the fax/modem means received a DCS, regardless of whether or not the fax/modem means has already received the TCF reception command from the AT command output means.
In accordance with a third aspect of the present invention, in the second aspect, the internal states of the fax/modem means includes an AT command standby state, an AT command execution state and an AT command provisional execution state. In the AT command standby state, the fax/modem means waits for supply of an AT command from the AT command output means. In the AT command execution state, the fax/modem means executes an AT command. The fax/modem means changes into the AT command provisional execution state as the state for receiving a TCF, just after receiving a DCS. In the AT command provisional execution state, the fax/modem means receives the TCF.
In accordance with a fourth aspect of the present invention, in the third aspect, the fax/modem means includes a TCF storage means for temporarily storing the TCF which is received in the AT command provisional execution state.
In accordance with a fifth aspect of the present invention, in the third aspect, the fax/modem means resets a timer which counts the duration of the AT command provisional execution state, when the fax/modem means received the DCS.
In accordance with a sixth aspect of the present invention, in the fourth aspect, the fax/modem means deletes the TCF stored in the TCF storage means when the fax/modem means received the DCS.
In accordance with a seventh aspect of the present invention, in the fourth aspect, the fax/modem means refers to a timer which counts the duration of the AT command provisional execution state in the AT command provisional execution state. The fax/modem means deletes the TCF stored in the TCF storage means and changes into the AT command standby state if the duration of the AT command provisional execution state has reached a predetermined length.
In accordance with an eighth aspect of the present invention, in the fourth aspect, the fax/modem means judges whether or not the TCF storage means is overflowing in the AT command provisional execution state. The fax/modem means deletes the TCF stored in the TCF storage means and changes into the AT command standby state if the TCF storage means is overflowing.
In accordance with a ninth aspect of the present invention, in the fourth aspect, the TCF stored in the TCF storage means is outputted to the AT command output means after the fax/modem means received the TCF reception command from the AT command output means.
In accordance with a tenth aspect of the present invention, there is provided a TCF reception method for a facsimile machine provided with a fax/modem means. The method comprises a TCF reception state transition step. In the TCF reception state transition step, the fax/modem means is changed into a state for receiving a TCF (Training Check Field) if the fax/modem means received a DCS (Digital Command Signal) regardless of whether or not the fax/modem means has already received a TCF reception command.
In accordance with an eleventh aspect of the present invention, there is provided a TCF reception method for a facsimile machine which is provided with a fax/modem means for communicating signals with a communication line in order to sending and receiving a fax and an AT command output means for outputting AT commands such as a DCS reception command for requesting reception of a DCS (Digital Command Signal) and a TCF reception command for requesting reception of a TCF (Training Check Field) to the fax/modem means. The method comprises a TCF reception state transition step. In the TCF reception state transition step, the fax/modem means is changed into a state for receiving a TCF if the fax/modem means received a DCS regardless of whether or not the fax/modem means has already received a TCF reception command from the AT command output means.
In accordance with a twelfth aspect of the present invention, in the eleventh aspect, the internal states of the fax/modem means includes an AT command standby state, an AT command execution state and an AT command provisional execution state. In the AT command standby state, the fax/modem means waits for supply of an AT command from the AT command output means. In the AT command execution state, the fax/modem means executes an AT command. The fax/modem means changes into the AT command provisional execution state as the state for receiving a TCF, just after receiving a DCS. In the AT command provisional execution state, the fax/modem means receives the TCF.
In accordance with a thirteenth aspect of the present invention, in the twelfth aspect, the method further comprises a TCF storage step in which the TCF received in the AT command provisional execution state is stored in a TCF storage means.
In accordance with a fourteenth aspect of the present invention, in the twelfth aspect, the method further comprises a timer reset step in which a timer which counts the duration of the AT command provisional execution state is reset when the fax/modem means received the DCS.
In accordance with a fifteenth aspect of the present invention, in the thirteenth aspect, the method further comprises a TCF deletion step in which the TCF stored in the TCF storage means is deleted when the fax/modem means received the DCS.
In accordance with a sixteenth aspect of the present invention, in the thirteenth aspect, the method further comprises a timer check step and a first deletion transition step. In the timer check step, the fax/modem means refers to a timer which counts the duration of the AT command provisional execution state and thereby checks the duration of the AT command provisional execution state. In the first deletion transition step, the TCF stored in the TCF storage means is deleted and the fax/modem means is changed into the AT command standby state if the duration of the AT command provisional execution state has reached a predetermined length in the timer check step.
In accordance with a seventeenth aspect of the present invention, in the thirteenth aspect, the method further comprises a TCF overflow check step and a second deletion transition step. In the TCF overflow check step, the fax/modem means checks whether or not the TCF storage means is overflowing. In the second deletion transition step, the TCF stored in the TCF storage means is deleted and the fax/modem means is changed into the AT command standby state if the TCF storage means is overflowing in the TCF overflow check step.
In accordance with an eighteenth aspect of the present invention, in the thirteenth aspect, the TCF stored in the TCF storage means is outputted to the AT command output means after the fax/modem means received the TCF reception command from the AT command output means.